(1) Field of the Invention
The invention relates to a method of fabricating a polycide gate structure, and more particularly, to a method of fabricating a polycide gate structure while preventing fluorine-induced gate oxide degradation in the manufacture of integrated circuits.
(2) Description of the Prior Art
Low pressure chemical vapor deposited (LPCVD) tungsten silicide (WSi.sub.x) has been widely used in the polycide gate structure. WF.sub.6 and SiH.sub.4 are the main reaction gases. A large number of fluorine atoms are incorporated into the tungsten silicide layer during the deposition process. The paper, "Direct Evidence of Gate Oxide Thickness Increase in Tungsten Polycide Processes" by S. L. Hsu et al, IEEE Electron Device Letters, Vol. 12, No. 11, November 1991, pp. 623-625, shows that the fluorine atoms "diffused from tungsten silicide films to gate oxides causes additional growth." This additional gate oxide will cause device degradation such as a shift in threshold voltage and a descrease in saturation current.